A metal-extrusion apparatus comprises essentially an extrusion press fed with pieces of metal to be extruded, called "billets", and consequently associated, on one side, with devices for preparing billets and, on the other side, with devices for discharging the extruded bars.
In general terms, the extrusion press comprises a crosshead connected, by means of columns, to a fixed cross-member and a moveable cross-member moveable in an extrusion direction under the action of the main jack bearing on the fixed cross-member. Located between the moveable cross-member and the crosshead is a container delimiting a tubular receptacle intended for the billet to be extruded and capable of being shut off at both its ends by means of two closing pieces, namely, a solid bottom, also called a dummy block, bearing on the moveable cross-member, and a die, also called a "die-body block", mounted on the support and bearing on the crosshead. The die defines the extrusion axis. Extrusion is caused as a result of the insertion inside the receptacle of an elongate rod of a length greater than that of the receptacle, called a "rammer" and carrying, at its end, one or the other of the closing pieces, depending on the extrusion method chosen.
In fact, a distinction can be made between two essential types of extrusion:
(1) direct extrusion, in which the container is stationary and bears on the crosshead carrying the die, the rammer bearing on the moveable cross-member and being equipped, at its end, with the dummy block which closes the container and which fits into the latter, thereby penetrating progressively into the receptacle in order to come nearer to the die, thereby causing the extrusion of the metal of the billet, and
(2) reverse extrusion, in which the container bears on the moveable cross-member carrying the bottom of the container and slips onto a fixed rammer bearing on the crosshead and carrying the die-body block at its end facing the container, the container being moved towards the crosshead by means of the moveable cross-member, at the same time slipping onto the rammer, the latter being provided with an axial orifice for the discharge of the bar formed in this way.
The invention to be described can be used in either of the two types of extrusion press.
It is possible to feed precut billets of constant length to the press, but the quantity of extruded metal obviously depends on the size of the billet and therefore may not meet the particular requirements. Consequently, in some cases, it is preferable to cut the billets to order, so that each billet has a size corresponding substantially to the bar length to be extruded, taking into account the butt which, at the end of extrusion, always remains between the dummy block and the die-body block.
In this case, the metal to be extruded takes the form of bars or "bits" which are cut to order at one end, to form a billet of desired length. Since the billet also has to be heated to the extrusion temperature, it is expedient to convey the metal bars through a heating furnace, at the end of which are located shears making it possible to cut billets of variable length matching the product length to be extruded. The shears themselves comprise means for holding the billet in a stand-by position after cutting and means for moving the cut billet from the stand-by position up to a position for loading into the press centered on the extrusion axis.
Normally, the bar heating furnace and the shears associated with it are placed next to the press, and the billet is transferred parallel to itself from the stand-by position to the loading position in a direction of movement transverse relative to the extrusion axis.
The means of holding the billet in the stand-by position often consist of a chute-like scoop which is associated with the shears and which supports the end of the bar during cutting and then assumes the stand-by position, for example as a result of a tilting movement.
Various means are used to ensure that the billet is transferred from the stand-by position to the loading position. For example, the scoop located at the outlet of the shears can discharge the cut billet onto a transverse conveyor which delivers the billet to a bucket located at the end of an arm capable of subsequently tilting in order to place the billet in the extrusion axis. The transfer from the stand-by position to the loading device can also take place by means of a gripper mounted on a transversely moveable support. Because the furnace and the shears have to be arranged at some distance from the press, it has therefore seemed obvious hitherto to use two separate transfer devices, on the one hand a device which, as has been seen, consists of a conveyor or a simple chute which delivers the billet from the stand-by position after cutting to a take-up position nearer the press and, on the other hand, a loading arm equipped with a bucket which, as a result of pivoting or a translational movement, transfers the billet from the take-up position to the loading position.
This handling of the billet by at least two transfer members via a take-up position increases the transfer times, but above all has disadvantages when the billet is in several pieces. In fact, as mentioned, it is often preferable to cut the billets to order from bars located in a heating furnace. The length of these bars does not normally correspond to an integral multiple of the length of the billet, and consequently, when the end of the bar is reached, the remaining piece can be either shorter than or longer than the normal length of the billet. If the remaining length is too small, this piece must be completed by an additional piece taken from the succeeding bar, and if the length is too great a small-size piece remains, and to avoid wasting this it has to be combined with an additional piece taken from the succeeding bar.
The transfer of a billet in several pieces from the stand-by position to the loading position presents difficulties, especially when the pieces are of small size, because they can assume a crosswise position in the various transfer members.
On the other hand, the billet must be introduced into the container axially and therefore, in the loading position, must be placed in a free space provided between one end of the receptacle and the corresponding closing piece. For this purpose, the bottom of its container or the container of the die-body block is moved aside axially, the billet being conveyed by the loading scoop into the space so formed and then being introduced inside the receptacle by sliding axially.
The press must therefore have an additional length, allowing the container to execute the movements necessary to provide the free loading space. However, the tendency in extrusion techniques is as far as possible to reduce the number and extent of the movements of the various components of the press, in order to reduce the overall time of the extrusion cycle, and moreover, in the light of the dimensions reached at the present time on extrusion presses, any decrease in the length of the press results in a considerable saving. Consequently, to reduce the length of the press, it has sometimes been proposed to slip the container onto the rammer, in such a way as to provide the free loading space between the rammer and the die, where direct extrusion is concerned, or between the rammer and the bottom of the container, where reverse extrusion is concerned.
To introduce the billet into the container, the latter can be held only at one end by means of the loading scoop, the other cantilevered end is then introduced into the receptacle of the container, and then, since the billet is held by the latter, the loading scoop can be withdrawn and the billet introduced into the receptacle by means of a loading jack or the rammer or as a result of the movement of the container.
It is quite clear that such a method of loading cannot be used when the billet consists of two separate pieces.
In another loading method, after the billet has been placed in the free space between the closing bottom of the container and the die-body block, these two components are controlled so as to be brought nearer to one another, the billet being gripped between them; the loading scoop can then be removed and the container shifted axially so as to slip onto the billet held in this way. Hitherto, it has not been possible to adopt such a loading method for a billet in two pieces which, with the devices used, could not be held in the extension of one another to slip easily into the receptacle of the container.